Abstract
Industrialized countries experience a population aging. Elderly patients, due to the experienced immunity, have a constant pro-inflammatory milieu. Little is known on how adaptive immunity impacts the tissue homeostasis and regeneration. The standardized housing of lab animals is specific pathogen free (SPF). However, this housing condition hinders antigen exposure and thus an aging of the adaptive immune system. We hypothesized that exposure to antigens and a developing adaptive immunity will impact tissue homeostasis and regeneration in mice. Mice kept under SPF housing or non-SPF were examined towards their immune status via flow cytometry, bone structure via microCT and bone competence via biomechanical torsional testing. MSCs from these mice were analyzed regarding their differentiation potential and ECM production under various immune cell signaling. Bone regeneration was analyzed in vivo in a mouse osteotomy model. The memory and effector compartment of the adaptive immunity was significantly increased in mice under non-SPF housing. This housing led to an increased femoral cortical thickness and torsional stiffness (p<0,05), whereas the tissue mineral density was not affected. The differentiation potential of stem cells under the influence of an aged immune milieu was significantly reduced. Bone formation was highly affected by the immune status and availed of a naïve immune cell milieu. Adaptive immunity directly impacts bone tissue formation, by exhibiting a constant stress, leading to structural differences in bone tissue organization as well as mechanical competence. For experimental settings, it appears highly relevant if mouse models have had the chance to develop an experienced immune system.
